Error screens for no connection to datahub - datahub is not responding

[murdo-moj]

• We don't do error handling that well
• For example, if the search call the datahub fails, there's a visible django traceback on find-moj-data
• check for existing patterns
• this is a custom informative error page for if the data_platform_catalogue library queries the GraphQL API and it has a 500 error. At the moment, we get the generic 500 error page for find-moj-data, which is uninformative as to if the frontend or backend has caused an error

[MatMoore]

How to customise the error view: https://docs.djangoproject.com/en/5.0/topics/http/views/#customizing-error-views

Examples: https://ron.sh/handling-custom-django-error-pages-the-proper-way/

[MatMoore]

Overriding the 500 handler won't work as we can't access the original exception there:

    # All handlers take (request, exception) arguments except handler500
    # which takes (request).

Django handles this here https://github.com/django/django/blob/94ab56ee2e24d4764296580da66dbbdc9ba03b02/django/core/handlers/exception.py#L140 https://github.com/django/django/blob/94ab56ee2e24d4764296580da66dbbdc9ba03b02/django/urls/resolvers.py#L731

So looks like we need to implement this as a middleware https://docs.djangoproject.com/en/5.0/topics/http/middleware/#process-exception